Bone rifling system and method of preparing a bone using such system

ABSTRACT

A bone rifling system for use in prosthesis, which allows improved prosthetic bone fixation. The system comprises orthopedic undercut reamer, which can cut controlled internal groove circles or spiral grooves on the internal surface of host bone. The system converts the commonly reamed smooth bone to grooved or rifled bony tube. Used together with bone cements, the bone rifling system ensures prosthetic bone fixation by significantly increasing the pull out strength, and decreasing the rate of clinical loosening and failure of replacement joints. Also disclosed is a method for preparing a bone for a prosthesis using such a bone rifling system to cut grooves in a host bone for increased prosthetic bone fixation.

The present application is a non-provisional utility application andclaims the benefit of Provisional Application No. 61/166,128, filed Apr.2, 2009, the contents of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to new bone rifling system (BRS) andmethod of using such system for prosthetic bone fixation. The inventiondiscloses a bone rifling system comprising an orthopedic undercutreamer, for use with bone cement to increase the fixation of a cementedbone implant, and also discloses a method of “rifling” the host bone.The reamer comprises a guide tube having a proximal and distal end, acutter bar having at least one cutter extending from a portion of saidcutter bar, the cutter bar positioned within the guide tube between theproximal and distal ends of the guide tube and displaceable to extendthe at least one cutter from an outer surface of guide tube, an engagerfor engaging the cutter for controlling the displacement of said cutterbar, and a cap for closing the proximal end of the guide tube. The bonerifling system that comprises the reamer and accessories candramatically improve prosthetic bone fixation by significantlyincreasing the pull out strength and decreasing the rate of clinicalloosening and failure of replacement joints. Using such a system toprepare the host bone represents an improvement in prostheticprocedures.

BACKGROUND OF THE INVENTION

Prosthesis, a medical term originated from the Greek word for“addition”, is an artificial extension that replaces a missing bodypart. In the case of an endoprosthesis, an artificial device is placedinside the body to replace the missing bodily part. This medicalprocedure has been widely used in many different situations. Forexample, endoprosthesis can be used in rebuilding joints, such asartificial hips and artificial knees. For another example,endoprosthesis has been applied to patients whose bones were amputated,including rebuilding cancer patients' limbs by creating anendoprosthetic bone and adjacent joint to replace the cancerous one.

In situations such as hip and joint replacement, wherein the prosthesisis designed to be fit or inserted into a bone, the replacements areoften fixed to bones by press fitting the prosthesis into the host bone,which has been filled with bone cement such as polymethylmethracylate(PMMA). Bone cement was first used in the 1950s. Since then, somemodifications have been made and alternatives have been developed to theoriginal PMMA cement. However, the general technique that uses bonecement for prosthesis has not changed significantly in over the past 40years. The common method of preparing the bone is to ream the bone witha bone reamer, and then inject bone cement into the medullary canal,then the prosthesis replacement is placed into the bone. The bone cementprovides for an immediate fixation, similar to filling a tooth cavity.This technique always results in a smooth bore cortical host bone.

These days, millions of procedures of this type are conducted all overthe world every year. However, a major clinical problem with such asystem of fixing the prosthesis implant lies in the ultimate looseningof the bone-cement interface overtime.

When the implant has loosened, the prosthesis may need revision orreplacement. In such case, the bone cement must be fully removed, andthe prosthesis previously implanted in the body is removed and replacedby a new prosthesis. Such replacement operations usually cause loss ofhealthy bone substances, and are often more complex and more difficultthan the original prosthesis operation. In addition, prosthesis revisionoperations are often more expensive for patients.

It has been found that there is rarely a loosening in the junctionbetween the prosthesis and the cement, that is, at the prosthetic-cementjunction. On the other hand, the main mechanism of loosening is thedevelopment of a loose interface between the bone and the implanted bonecement (PMMA). This problem can be solved by preparing the bone througha different method, using the new bone rifling system disclosed herein.

In using the common technique of reaming, the reaming results in theremaining bone being essentially a smooth, cortical, bony tube, withsmooth internal surface, regardless of how the cement is mixed orimplanted. Thus, there is minimal interdigitation of the cement into thebone. In addition, any interdigitation of the cement that may occurweakens over time, and the prosthesis is thus disconnected from theinterior surface of the bone, resulting in the need to surgically resetthe prosthesis.

Accordingly, there is a need to provide a system which increasesprosthetic bone fixation, reliably secures the prosthesis with respectto the bone, thereby eliminating the need to conduct further surgery asthe bone-cement interface does not deteriorate over time. There is alsoa need to use the new system to prepare the host bone in prosthesis.

SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide a new bonerifling system (BRS) for unique prosthetic bone fixation. The systemcomprises an orthopedic undercut reamer for use together with bonecement to increase the fixation of a cemented bone implant. The bonerifling system comprises the reamer and optional accessories to cutgrooves on the internal surface of a host bone before bone cement isadded. The grooved internal bone surface dramatically improvesprosthetic bone fixation between the bone and the bone cement, bysignificantly increasing the pull out strength, thus decreasing the rateof clinical loosening and failure of replacement joints. This system canbe used to convert the smooth bore bone (bony tube) of the commonlyreamed bone to a grooved or rifled endosteal surfaced bony tube.

In one embodiment of the invention, the disclosed new bone riflingsystem comprising the undercut reamer can cut controlled, deep, internalgroove circles on the internal surface of a host bone.

In another embodiment of the invention, the disclosed bone riflingsystem comprising the reamer can cut spiral grooves analogous tostandard rifle grooves on the internal surface of a host bone.

The undercut reamer is an instrument that can be used in orthopedicsurgery, to create one or multiple undercuts (negative ridges) in thebone to provide enhanced fixation for endoprosthetic implants whichutilize bone cement such as PMMA. The new bone rifling system (BRS)disclosed presently applies the undercut reamer to provide a groovedinternal bone surface for device implantation, thus improves theintegrity of the bone fixation. Specifically, the undercut surfaceprepared by the BRS strengthens bone-cement interface, thereby increasesthe pull out strength of the implant. Compared to the smooth internalsurface of bone, prepared by the traditional method, the new BRS systemcan reduce incident of loose interface between the bone and theimplanted bone cement such as PMMA, thus benefits patients who undergoprosthetic procedures. This improvement is accomplished by creating apositive lock for the fixation material into the bone.

Further, the invention provides a method of preparing a host bone forprosthesis, using the bone rifling system (BRS) disclosed in the presentinvention. The method can improve prosthetic bone fixation and decreasethe rate of clinical loosening and failure in endoprosthesis, bysignificantly increasing the pull out strength, through convertingsmooth bore bone to a grooved or rifled bony tube. The method comprisesusing the BRS comprising unique orthopedic undercut reamer and optionalaccessories to cut circular or spiral grooves on the internal surface ofhost bone, then retract the reamer before adding cement to the bone, toincrease fixation between the bone and the cement, for endoprostheticimplants which utilize bone cement such as PMMA.

In one embodiment of the disclosed bone preparation method, the undercutreamer can cut controlled, deep, internal groove circles on the internalsurface of a host bone.

In another embodiment of the disclosed bone preparation method, theundercut reamer can cut spiral/rifling grooves analogous to standardrifle grooves on the internal surface of a host bone.

The disclosed bone rifling system allows the reamer to be placed intothe intramedullary canal. The reamer includes a cutter in the form ofcutting teeth. Once the reamer is positioned correctly, the cuttingteeth can be extended to engage the internal bone surface. Once thecutting teeth are extended a drive mechanism is mounted on the portionof the undercut reamer outside of the bone (such as a universal adapter)so that the cutter can be rotated by hand or external power, therebycreating the undercuts at the level of the cutting teeth. This bonerifling system has an additional mechanism which permits the bone debrisformed by the undercut reaming or rifling to be continuously irrigatedand suctioned to remove all debris. This mechanism permits accurate andsafe reaming (i.e. to avoid stress fractures) during the undercuttingprocess. Once completed, the drive mechanism is removed and the cuttingteeth are retracted and disengaged from the internal bone surface,allowing the undercut reamer to be removed from the bone withoutdisturbing the undercuts (negative ridges) created by the reamer. Oncethe bone rifling system is removed from the bone, it can be completelydisassembled, cleaned and sterilized. Additional one or more of thecomponents of the system may be disposable, particularly the cutter.

The undercut reamer used in carrying out the improved prosthesisprocedure consists of multiple components. A cutter may be comprised ofmultiple cutting surfaces (teeth) that may be angled away from a cap.The cutter may fit within a guide tube, and contain pins that can slidethrough the side openings of the guide tube to allow the cutter to moveinside the guide tube in a controlled path. The guide tube has a slimcylinder shape that allows it to be inserted into the medullary canal ofvarious length, for example, for long bones such as the humerus, tibiaor femur. The multiple cutting surfaces (teeth) align with openings onthe guide tube for the cutting teeth to extend through in order toengage with the internal surface of bones. Once the cutting teeth areengaged, the universal adapter on the end of the reamer, which staysoutside of the bone, can be connected to an outside power source, torotate the cutter, which allows the cutting teeth on the cutter tocreate grooves on the engaged bone surface. The grooves can be eithercircular or spiral, depending on how the reamer is positioned and usedduring the cutting process. After the undercut is created, the cuttingteeth are then retracted through the openings The angled cutting teethmay assist in the removal of the cutter. The cutter can either be singleuse/disposable or multi-use. In either case the cutter is to be made ofa sterilizable material such as cobalt chrome or other known material.

A cutter extension tube or mechanism to extend the cutter into the bonecan consist of several different mechanisms so as to extend the cuttercomponent into the bone. One example would be a rod having a D shapedcross-section, which fits within the guide tube, with the flat portionmating up against the cutter. When the D shaped rod is forced down intothe guide tube, the multiple cutting surfaces are pushed into the bone.Removal of the D shaped rod allows the cutter to be removed.Alternatively, a cam shaped rod, which fits within the guide tube havingan increasing cross-section initially allows the cutter to be insertedwith ease. Once the cutter is in place the cam shaped rod is turned toapply pressure to the cutter and the opposite sidewall of the tube,allowing the cutting surfaces to be extended into the bone. Once theundercuts are completed the cam shaped rod would be turned to remove theforce against the cutter and would allow the cutter to be retracted andremoved from the tube. In another option, the cutter bar can be a flatplate that is positioned between two semi-cylinders, with the plate ofthe cutter bar including pins extending therefrom which engage slots oropenings in the semi-cylinders which act as cam surfaces to extend thecutter blades from a side of the guide tube. When the cutter bar ispushed by force, the pins can move through the guide tube as directed bythe slots, which allows the cutter bar to move radially away from acentral axis of the guide tube towards the periphery of the guide tube,thus allowing the cutting teeth to extend out through openings on theguide tube.

A pressurized membrane, which fits within the guide tube, could also beemployed. With the membrane deflated the cutter can be placed within thetube. Once the cutter is in place, the membrane would be pressurized andfilled with a saline solution. As the pressure of the membrane againstthe cutter increases, the cutter will be extended into the bone. Oncethe undercuts are completed the membrane would be decompressed and wouldallow the cutter to be retracted from the bone and removed from thetube.

The guide tube is provided to allow proper placement of the cutterwithin the intramedullary canal. The guide tube will come in multiplediameters and lengths to enable appropriate sizing for multiple sizecanals. The guide tube is provided with openings to allow the cuttingteeth to be extended and retracted through the tube, thus helping thereamer to get into and out of the bone. The guide tube may also containa continuous suction-irrigation tube as well as an external port andconnection therein to permit the extraction of debris from the cuttingprocess. The continuous suction-irrigation system being similar to thosecurrently used in connection with various bone reaming devices.

In an initial embodiment, a cap is mechanically fastened to the guidetube once the cutter has been extended into the bone, locking the cutterin place. The external portion of the cap will include a shank/quickdisconnect allowing use with variable power assisted and manual drills.Alternatively, the external portion of the reamer will include anengager which can be pushed toward the cap to apply pressure on thecutter bar and move the cutter bar inside the guide tube to make thecutting teeth extend out. The external portion of the reamer will alsoinclude a universal adapter that can be connected to outside powersource to rotate the cutter for cutting the internal surface of bone.Once the cutting teeth are extended through the openings of the tube andengage to the internal surface of bone, the guide tube and cutter arerotated to cut either the “O” ring grooves or spiral grooves into theinterior surface of the bone. After the undercut reamer has beenextended into the bone and the cuts made, the cap is unfastened from theguide tube allowing the extension mechanism and cutter to be retractedfrom the guide tube and the guide tube to be retracted from the bone; orthe engager is released and moves away from the cap to allow the cuttingteeth to retract.

A detailed description is given in the following embodiments withreference to the accompanying drawings. Advantages and features of thepresent invention will become more apparent from the following detaileddescription of the present invention when viewed in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts.

FIG. 1A is a partial cross-sectional view and FIG. 1B is a lateralcross-sectional view of the undercut reamer in accordance with thepresent invention.

FIGS. 2A and 2B are side and end views of the guide tube.

FIGS. 3A and 3B are side and end views of the cutter in accordance withone embodiment of the invention.

FIGS. 4A and 4B are side and end views of the extension tube mechanismin accordance with one embodiment of the invention.

FIGS. 5A and 5B are side and end views of the cutter in accordance withanother embodiment of the invention.

FIGS. 6A and 6B are side and end views of the extension tube mechanismin accordance with another embodiment of the invention.

FIG. 7 is a perspective view of the undercut reamer assembly inaccordance with an alternative and preferred embodiment of the presentinvention.

FIG. 8 is an exploded perspective view of the internal structure of theundercut reamer of FIG. 7.

FIG. 9 is a cross-sectional view of a portion of the interior of theundercut reamer of FIG. 7.

FIG. 10 is a perspective view of a cutter bar to be positioned in theundercut reamer of FIG. 7.

FIG. 11 is a schematic side view of the spring-assist for the cuttingteeth extension structure of the present invention.

FIG. 12 is a side view of the bone rifling system (BRS) of the presentinvention.

FIG. 13 is an expanded view of the guide tube of the bone rifling system(BRS) of the present invention in the unengaged state.

FIG. 14 is a further expanded view of the guide tube of the bone riflingsystem (BRS) of the present invention in the engaged state wherein thecutting teeth extend out through openings in the guide tube of theundercut reamer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As noted hereinabove, by forming controlled, deep, internal ridges onthe host bone by way of a series of internal ‘O’ rings or aspiral/rifling groove using an undercut reamer and its system of usewill increase dramatically the pull out strength and decrease the rateof clinical loosening and failure of replacement joints. This techniqueconverts the smooth bore bone (bony tube) of the commonly reamed bone toa grooved or rifled endosteal surfaced bony tube.

In accordance with the present invention as illustrated in FIGS. 1-6,the undercut reamer 10 is an instrument to be used in orthopedicsurgery, to create one or multiple undercuts (negative ridges) in thebone to provide enhanced fixation for endoprosthetic implants whichutilize bone cement. Providing an undercut surface for deviceimplantation improves the integrity of the bone/prosthetic fixation;specifically, the bone-cement interface, thereby increasing the pull outstrength of the implant. This is accomplished by creating a positivelock for the fixation of material into the bone.

The bone rifling system and method of preparing a bone using such systemincludes an undercut reamer 10 which consists of multiple components,and allows the reamer to be placed into the intramedullary canal andonce positioned correctly, has cutters 12 that are extended into thebone. Once the cutters 12 are extended, a chuck 14 is mounted on theportion of the undercut reamer outside of the bone so that it can berotated by hand or power thereby creating the undercuts at the level ofthe cutters. This tube may have an additional mechanism which permitsthe bone debris formed by the undercut reaming or rifling to becontinuously irrigated and suctioned to remove all debris (not shown).This permits accurate and safe reaming (i.e. to avoid stress fractures)during the undercutting process. Once completed, the chuck 14 is removedand the cutters 12 are extracted allowing the undercut reamer 10 to beremoved without disturbing the undercuts (negative ridges) created bythe reamer. Once the total undercut reamer construct is removed from thebone, it can be completely disassembled, cleaned and sterilized. Suchdisassembly could include the guide tube being divided into two halves.Further, one or more of the components of the undercut reamer may bedisposable, particularly the cutters 12.

The undercut reamer 10 used in carrying out the method consists ofmultiple components. The cutter 12 may be comprised of multiple cuttingsurfaces 16 that are angled away from the cap 14 and fit within a guidetube 18 which has been inserted into the medullary canal of variouslength long bones such as the humerus, tibia or femur. The multiplecutting surfaces 16 align with holes or openings 20 in the guide tube,which provide an opening for the cutting surfaces to extend through.Once the undercut is created the cutting surfaces 16 are then retractedthrough the guide holes 20. The angled cutting surfaces assist in theremoval of the cutter. The cutter can either be single use/disposable ormulti-use. In either case the cutter is to be of a sterilizable materialsuch as cobalt chrome or other known material.

Alternatively, the undercut reamer 10 may include a cutter 12′ asillustrated in FIGS. 5A and 5B. The cutter 12′ includes only a singlecutter surface 16′ which extends at an angle such that as the undercutreamer is rotated and withdrawn from the bone, the cutter surface 16′forms a spiral or rifle groove in the interior surface of the bone.

A cutter extension tube or mechanism to extend the cutter into the bonemay consist of several different mechanisms so as to extend the cuttercomponent into the bone. One example would be a rod 22 having a D shapedcross-section illustrated in FIGS. 4A and 4B, which fits within theguide tube 18, with the flat portion mating up against the cutter asshown in FIG. 1A. The D-shaped rod 22 is sized such that when the Dshaped rod 22 is forced down into the guide tube 18, the multiplecutting surfaces 16 are pushed into the bone. Removal of the D shapedrod 22 allows the cutter to be removed. Alternatively, a cam shaped rod24 as shown in FIG. 6A and 6B, which fits within the guide tube havingan increasing cross-section initially allows the cutter to be insertedwith ease. Once the cutter is in place the cam shaped rod 24 is turnedto apply pressure to the cutter and the opposite sidewall of the tube,allowing the cutting surfaces to be extended into the bone. Once theundercuts are completed the cam shaped rod 24 would be turned to removethe force against the cutter and would allow the cutter to be retractedand removed from the tube.

A pressurized membrane (not shown), which fits within the guide tubecould also be employed. With the membrane deflated the cutter can beplaced within the tube. Once the cutter is in place, the membrane wouldbe pressurized and filled with a saline solution. As the pressure of themembrane against the cutter increases, the cutter will be extended intothe bone. Once the undercuts are completed the membrane would bedecompressed and would allow the cutter to be retracted from the boneand removed from the tube.

The guide tube 18 is provided to allow proper placement of the cutter 12within the intramedullary canal. The guide tube 18 will come in multiplediameters and lengths to enable appropriate sizing for multiple sizecanals. The guide tube will be provided with at least one and likelymultiple openings 20 to allow the cutters to be extended and retractedthrough the tube and into and out of the bone. The guide tube 18 willalso contain a continuous suction-irrigation tube as well as an externalport and connection therein to permit the extraction of debris from thecutting process. The continuous suction-irrigation system (not shown)being similar to those currently used in connection with various bonereaming devices.

The cap 14 is mechanically fastened to the guide tube once the cutterhas been extended into the bone, locking the cutter in place. Theexternal portion of the cap will include a shank/quick disconnect 26allowing use with variable power assisted and manual drills (not shown).Once the cutter extensions are extended into the bone, the guide tube 18and cutters 16 are rotated to cut the “O” ring grooves or rifling intothe interior surface of the bone. After the undercuts have been extendedinto the bone and the cuts made, the cap is unfastened from the guidetube allowing the extension mechanism and cutter to be retracted fromthe guide tube and the guide tube to be retracted from the bone.Alternatively, when using the rifling cutter 12′ as shown in FIGS. 5Aand 5B, the guide tube 18 may be withdrawn from and inserted into thebone as the guide tube 18 and cutter 16′ are rotated to form asubstantially continuous spiral/rifle groove in the inner bone surface.

As noted hereinabove, by cutting controlled internal ridges and grooveson the host bone, the bone rifling system (BMS) converts the smooth boreinternal surface of the commonly reamed bone (bony tube) to a grooved orrifled endosteal surfaced bony tube. The system comprises an orthopedicundercut reamer that can be used to cut the grooves on bones to increasethe fixation between the bone and the cement, thus prevent loosening ofcemented bone implant. The bone rifling system that comprises the reamerand optional accessories can dramatically improve prosthetic bonefixation by significantly increasing the pull out strength anddecreasing the rate of clinical loosening and failure of replacementjoints.

In accordance with the present invention, the undercut reamer 10 is aninstrument to be used in orthopedic surgery, to create one or multipleundercuts (negative ridges) on the internal surface of bone to provideenhanced fixation for endoprosthetic implants which utilize bone cement.Providing an undercut surface for device implantation improves theintegrity of the bone/prosthetic fixation, specifically the fixation ofthe bone-cement interface. Therefore, the disclosed new bone riflingsystem increases the pull out strength of the implant by creating apositive lock for the fixation of material into the bone.

A preferred embodiment of the present invention will now be discussedwith respect to FIG. 7-14. As illustrated in FIG. 7, the preferred BoneRiffling System (BRS) includes a bone undercut reamer 100 having a guidetube 118. In accordance with the preferred embodiment, and particularlythe undercut reamer of FIGS. 7 and 8, the cutter bar 110 is a flat barthat fits within the guide tube 118 and includes pins 140, 141 that fitwithin the openings or cam slots 117 formed in positioningsemi-cylinders 142, 143. The slots 117 will be discussed in greaterdetail hereinbelow with reference to FIG. 9. When the semi-cylinders142, 143 are pushed by force, the pins on the cutter bar move throughthe guided path as directed by the cam slots 117, which allows thecutter bar 110 to move away from the central axis of the guide tube 118towards the peripheral edge of the tube, thus forcing the cutting teeth116 to extend out through opening(s) 120 formed in the guide tube 118.

The guide tube 118 is provided to allow proper placement of the cutterbar 110 within the intramedullary canal. The guide tube 118 may come inmultiple diameters and lengths to enable appropriate sizing for multiplesize canals. The guide tube 118 will be provided with at least one andlikely multiple openings 120 to allow the cutters 116 of the cutter bar110 to be extended and retracted through the guide tube 118 and into andout of the bone. Like the previous embodiment, the guide tube 118 mayalso contain a continuous suction-irrigation tube as well as an externalport and connection therein to permit the extraction of debris from thecutting process. The continuous suction-irrigation system (not shown)being similar to those currently used in connection with various bonereaming devices.

The undercut reamer 100 illustrated in FIGS. 7 and 8 includes a cap 114which is mechanically fastened to the guide tube 118 by way of one ormore hex set screws 119. The cap 114 is secured to and may be formedintegral with a shank 125 and slidably received a pair of engager rods132, 133, the significance of which will be explained in greater detailhereinbelow. Formed on an extended portion of the shank 125 is asurfaced area 126 which receives a quick connect of a drive device (notshown). This drive device may be a variable power assisted or manualdrill (again, not shown).

The engager rods 132, 133 are secured to or formed integrally with anengager 130. The engager 130 may be of an enlarged disc which allows forease in pushing the engager rods 132, 133 through the cap 114 and intocontact with the semi-cylinders 142, 143 in order to displace thesemi-cylinders 142, 143 toward a distal end of the guide tube 118. Aforce dispersing disc 131 may be positioned between the ends of theengager rods 132, 133 and the end surface of the semi-cylinders 142, 143in order to better transfer the force exerted by the engager rods 132,133 to the semi-cylinders 142, 143 to aid in the simultaneous movementof the semi-cylinders 142, 143 through the guide tube 118. Once theengager rods 132, 133 are fully inserted into the guide tube 118 throughthe cap 114, the engager is secured in place by way of at least one hexset screw 135. In doing so, the semi-cylinders 142, 143, maintain thecutters 116 of the cutter bar 110 in the extended position. Once thecutters 116 are extended into the bone, the guide tube 118 and cutters116 are rotated to cut “O” ring grooves or rifling into the interiorsurface of the bone. After the undercuts have been formed in the bone,the engager is released by unscrewing the hex set screw 135 whichpermits the engager rods 132, 133 to be retracted from the guide tube118 and thus permits the semi-cylinders 142, 143 to return to theiroriginal position due to a force from a coil spring 150 (discussed ingreater detail hereinbelow) thereby retracting the cutters 116 from thebone and back into the guide tube 118 due to the influence of the camslots 117 on the pins 140, 141. Thereby permitting the guide tube to bereadily removed from the intramedullary canal. Alternatively, when it isdesired to form a spiral undercut in the bone, the undercut reamer 110may be retracted during the rotation of the reamer and stopped wheredesired. If the reamer is not fully rotated out of the intramedullarycanal, the above procedure of retracting the cutters 116 can be carriedout at any time to remove the reamer from the intramedullary canal.

As shown in FIG. 8, and as discussed hereinabove, the external portionof the reamer 100 includes an engager 130 having a pair of engager rods132, 133 which extend through the cap 114 and into the guide tube 118,to apply pressure on the semi-cylinders 142, 143, and move the cutterbar 110 inside the guide tube to force the cutters 116 to extend outthrough the opening(s) 120. Once the cutters 116 are extended throughthe opening(s) 120 of the guide tube 118 and engage to the internalsurface of the intramedullary canal of the bone, the guide tube 118 andcutters 116 are rotated to cut either the “O” ring grooves or spiralgrooves into the interior surface of the bone.

The internal structure of the reamer 100 is further illustrated in FIG.9, which shows a partial cross-sectional view of the undercut reamer100. Specifically, the undercut reamer 100 is cut-in-half through theelongated axis, with the top half removed to reveal the internalstructure. In particular, FIG. 9 shows the guide tube 118 and one of thesemi-cylinders 142. As is readily apparent from FIG. 9, thesemi-cylinder 142 includes a plurality of cam slots 117 which are formedtherein and receive the pins 140, 141 of the cutter bar 110 (not shown).As can be appreciated, because the cam slots 117 are positioned at anangle with respect to the central axis of the guide tube 118, as thesemi-cylinders 142, 143 are moved in the axial direction of the guidetube 118, the pins 140, 141 of the cutter bar 110 will be driven towardsthe periphery of the guide tube 118 thus forcing the cutters 116 towardsthe periphery of the guide tube 118 and out through the opening(s) 120formed therein. Also shown in FIG. 9 is the coil spring 150. Thespecific structure of the coil spring 150 will be discussed in greaterdetail hereinbelow with respect to FIG. 11.

A perspective view of the cutter bar 116 is shown in FIG. 10. The figureshows 3 sets of pins 140, 141 and 3 cutters 116. As can be readyappreciated, any number of pin sets and cutters can be used and thenumber of pin sets need not equal the number of cutters. Further, whilethe pins are illustrated as being in sets extending collinear with oneanother, the sets may be offset from one another or even extend fromonly one side of the cutter bar 110. Additionally, and end 146 of thecutter bar 110 is of a reduced dimension. This enables the end 146 toextend beyond the semi-cylinders and through the coil spring 150 andinto contact with a stop 151 positioned in the distal end of the guidetube 118. This feature will be explained in greater detail hereinbelowwith respect to FIG. 11.

The semi-cylinders 142 and 143 as well as the cutter bar 110 can onlymove within a limited range inside the guide tube 118. FIG. 11 is aperspective view of the guide tube 118 in an opened-up condition similarto FIG. 9 including the cutter bar 110 positioned therein. The springassist mechanism includes the coil spring 150 and stop 151. Thesemi-cylinders 142, 143 are displaced within the guide tube 118 andpositioned against the spring assist mechanism and particularly the coilspring 150. The coil spring 150 resists movement of the semi-cylinders142, 143 inside the guide tube 118 when the semi-cylinders are movedtowards the distal end of the guide tube 118. The coil spring 150 alsoprovides a force for directing the semi-cylinders 142, 143 away from thedistal end of the guide tube 118 when the cutters 116 are to beretracted into the guide tube 118 for removal of the device.

As noted from FIG. 11, the reduced end 146 of the cutter bar 110 ispositioned in contact or at least close proximity to the stop 151 andthe pins 140 are positioned within the slots 117. In doing so, when aforce is applied to the semi-cylinders 142, 143 in the axial directionof the guide tube 118, the reduced end 146 of the cutter bar 110contacts the stop 151 to prevent axial movement of the cutter bar 110such that the cutter bar 110 is moved laterally toward the periphery ofthe guide tube 118 by way of the pins 140, 141 which move throughcorresponding cam slots 117 formed in the semi-cylinders 142, 143. As aresult, when the engager is pushed down, the cutter bar 110 moveslaterally within the guide tube 118 and towards the periphery of thetube, thereby the cutters 116 on the cutter bar 110 extend out throughthe opening(s) 120 of the guide tube 118.

As with most surgical instruments, a majority of the undercut reamer 100is made of stainless steel. However, any known material which is ofsufficient strength to endure the stress placed on the device when inuse and that can be readily cleaned and sterilized after each use may beemployed. Such disassembly could include the guide tube 118 beingdivided into two halves. Further, one or more of the components of theundercut reamer may be disposable, particularly the cutter bar 110.

Similar to the device illustrated in FIGS. 7-11, FIGS. 12-14 illustratea slightly modified embodiment of the present invention. Similar to thatdiscussed above, the undercut reamer 200 is formed primarily ofstainless steel; however, other known materials which are of sufficientstrength to endure the stress placed on the device when in use and thatcan be readily cleaned and sterilized after each use may be used. Suchdisassembly could include the guide tube being divided into two halves.FIG. 12 illustrates the undercut reamer 200 of the bone rifling system(BRS) in accordance with the present invention. Like the device of FIG.7, the undercut reamer 200 set forth in FIGS. 12-14 includes multiplecomponents which allow the reamer to be placed into the intramedullarycanal and once positioned correctly, can cut either circular or spiralundercuts in the inner wall of the bone. The undercut reamer 200includes a guide tube 218. In accordance with this embodiment, thecomponents positioned in the interior of the guide tube 218 aresubstantially identical to those discussed with respect to FIGS. 7-11.Particularly, the undercut reamer 200 of FIGS. 12-14 includes a cutterbar which is a flat bar that fits within the guide tube 218 and includescutters 216 and pins that fit within the openings or cam slots formed inpositioning semi-cylinders. As with the previous embodiment, when thesemi-cylinders are pushed by force toward the distal end of the device,the cutter bar is maintained in its axial position and the pins of thecutter bar move through the guided path as directed by the cam slots,which allow the cutter bar to move away from a central axis of the guidetube 218 towards the peripheral edge of the guide tube 218, thus forcingthe cutters 216 from the retracted position illustrated in FIG. 13 tothe extended position illustrated in FIG. 14, wherein the cutters 216 toextend out through openings 220 formed in the guide tube 218.

Like the previous embodiment, the guide tube 218 is provided to allowproper placement of the cutter bar within the intramedullary canal. Theguide tube 218 may come in multiple diameters and lengths to enableappropriate sizing for multiple size canals. The guide tube 218 isprovided with multiple openings 220 to allow the cutters 216 of thecutter bar to be extended and retracted through the guide tube 218 andinto and out of the bone. Like the previous embodiment, the guide tube218 may also contain a continuous suction-irrigation tube as well as anexternal port and connection therein to permit the extraction of debrisfrom the cutting process. The continuous suction-irrigation system (notshown) being similar to those currently used in connection with variousbone reaming devices.

The undercut reamer 200 illustrated in FIG. 12 includes a cap 214 whichis mechanically fastened to the guide tube 218 by way of one or more hexset screws 219. The cap 214 is secured to and is preferably formedintegrally with a shank 225. The cap 214 slidably receives a pair ofengager rods 232, 233, the significance of which is similar to that ofthe previous embodiment and will be explained in greater detailhereinbelow. The free end of the shank 225 receives a quick connect of adrive device (not shown). This drive device may be a variable powerassisted or manual drill (again, not shown).

The engager rods 232, 233 are secured to or formed integrally with anengager 230. The engager 230 may be of an enlarged disc which allows forease in pushing the engager rods 232, 233 through the cap 214 and intocontact with the semi-cylinders positioned inside the guide tube 218 inorder to displace the semi-cylinders toward a distal end of the guidetube 218. A locking ring 238 is also positioned on the shank 225 inorder to maintain the cutters in their extended position. The lockingring 238 includes at least one hex set screw received in screw hole 240in order to maintain the position of the locking ring 238 along theshank 225. A force dispersing disc (not shown) may be positioned betweenthe ends of the engager rods 232, 233 and the end surface of thesemi-cylinders in order to better transfer the force exerted by theengager rods 232, 233 to the semi-cylinders to aid in the simultaneousmovement of the semi-cylinders through the guide tube 218.

The enlarged disc forming the engager 230 may be of a single piece or ofa two piece construction wherein the engager 230 has an inner disc whichis fixedly secured to the engager rods 232, 233 and an outer disc whichrotatably receives the inner disc. In doing so, during the rotation ofthe undercut reamer device 200, the outer disc can be held stationarythereby leaving the inner disc which is integral with the engager rods232, 233 which are extend through the cap 214 and into the guide tube218 to rotate as directed by the power assist mechanism or manual drill.A handle 244 may also be positioned on the guide tube 218 to assist inmanipulating the device.

In use, the undercut reamer 200 and particularly the guide tube 218 ofthe undercut reamer 200 is inserted into the intramedullary canal.During this insertion, the cutters 216 are in the retracted position.Once the guide tube is properly positioned within the intramedullarycanal, the engager rods 232, 233 are forced into the guide tube 218through the cap 214 by pushing forward on the engager 230. Once theengager rods 232, 233 are extended a desired distance into the guidetube 218 and the cutters are extended a desired distance from the guidetube 218, the engager 230 is secured in place by way of the locking ring238 by the hex set screw. In doing so, the semi-cylinders, maintain thecutters 216 of the cutter bar in the extended position. Once the cutters216 are extended into the bone, the guide tube 218 including the cutters216 are rotated to cut “O” ring grooves or rifling into the interiorsurface of the bone. It should be noted that the distance in which thecutters 216 extend from the guide tube 218 is dependent on both thelength of the cutters 216 as well as the distance in which thesemi-cylinders are displaced in the axial direction of the guide tube218. This displacement may also be controlled by the distance in whichthe engager rods 232, 233 are inserted into the guide tube. Accordingly,the user may readily adjust the amount of penetration the cutters 216make into the intramedullary canal.

After the undercuts have been formed in the intramedullary canal of thebone, the engager 230 is released by unscrewing the hex set screwmaintaining the locking ring 238 in place, which permits the engagerrods 232, 233 to be retracted from the guide tube 218 and thus permitsthe semi-cylinders to return to their original position due to a forcefrom a coil spring positioned in the distal end of the guide tube 218,similar to that illustrated in FIG. 11. In doing so, the cutters 216 areretracted from the bone, back into the guide tube 218 due to theinfluence of the cam slots of the semi-cylinders and the pins of thecutter bar, similar to that of the previous embodiment, therebypermitting the guide tube to be readily removed from the intramedullarycanal. Alternatively, when it is desired to form a spiral undercut inthe bone, the undercut reamer 200 may be retracted during the rotationof the reamer and stopped where desired. If the reamer is not fullyrotated out of the intramedullary canal, the above procedure ofretracting the cutters 216 can be carried out at any time to remove thereamer from the intramedullary canal.

The present invention also provides a method for unique prosthetic bonefixation using the disclosed new bone rifling system (BRS). The methodcomprises the steps of using the BRS to cut circular or spiral grooveson the internal surface of the bone, remove the reamer and also removethe debris generated during the cut, placing a desired implant in thebone, and placing cement in the bone to secure the implant to the bone.More specifically, the method comprises inserting the orthopedicundercut reamer into the desired location inside the bone, pushing theengager by hand or using other means to move the engager rods forward toforce the cutter bar laterally through the guide tube by forcing thepins of the cutter bar to move through the guided path formed by theslots in the semi-cylinders to extend the cutters through openingsformed in the guide tube, engage the cutting teeth with the internalsurface of the bone, connect a universal adapter to a power source,rotate the cuter bar to allow the cutting teeth to cut grooves on theinternal surface of the bone, continuously irrigating and suctioning thedebris formed by the undercut reaming or rifling to permit accurate andsafe reaming and avoid stress fractures during the undercutting process.Then retracting the cutters to disengage from the bone after the cuttingis complete, allowing the undercut reamer to be removed withoutdisturbing the undercuts (negative ridges) created by the reamer, andfinally placing a desired implant in the bone and placing cement in thebone to secure the implant to the bone.

While the foregoing invention is described with reference to severalembodiments, the present invention may be practiced otherwise withoutdeparting from the spirit and scope of the invention. While variousembodiments in accordance with the present invention have been shown anddescribed, it is understood that the invention is not limited thereto.The present invention may be changed, modified and further applied bythose skilled in the art. Therefore, this invention is not limited tothe detail shown and described previously, but also includes all suchchanges and modifications.

I claim:
 1. A method of preparing bone for a prosthesis, comprising:providing a bone rifling system for cutting circular or spiral grooveson an internal surface of a host bone, said bone rifling systemincluding an undercut reamer, the undercut reamer having: a guide tubehaving a proximal and distal end, a cutter bar having at least onecutter extending from a portion of said cutter bar, said cutter barbeing positioned within said guide tube between the proximal and distalends of said guide tube and displaceable to extend said at least onecutter from an outer surface of said guide tube, an engager having atleast one engagement rod and adapted to control the displacement of saidcutter bar and to engage the cutter with the internal surface of thebone, and at least one semi-cylinder positioned within the guide tubeand adapted to displace said cutter bar in response to movement of saidat least one engagement rod; positioning said undercut reamer within anintramedullary canal of the bone; extending the at least one cutter froma surface of said undercut reamer; rotating said undercut reamer andsaid cutter to form an undercut in the intramedullary canal of the bone;retracting said at least one cutter to a position within the surface ofsaid undercut reamer; and removing said undercut reamer from theintramedullary canal of the bone.
 2. The method of claim 1, furthercomprising placing cement in the intramedullary canal of the bone tosecure the implant to the bone.
 3. The method of claim 1, furthercomprising removing debris generated during the undercutting process. 4.The method of claim 1, wherein the undercut reamer for cutting circularor spiral undercut groove in the intramedullary canal of the bonecomprises: a cap for closing the proximal end of the guide tube.
 5. Themethod of claim 4, wherein the at least one engagement rod extends fromsaid engager through said cap and is in contact with said at least onesemi-cylinder.
 6. The method of claim 5, wherein the undercut reamerincludes a pair of semi-cylinders having said cutter bar positionedbetween said semi-cylinders and said engager includes at least twoengagement rods.
 7. The method of claim 6, wherein said cutter barincludes at least one guide pin and at least one of said semi-cylindersincludes at least one guide slot such that said at least one guide slotreceives said at least one guide pin for controlling the displacement ofsaid cutter bar.
 8. The method of claim 7, wherein said cutter barincludes a plurality of guide pins and said semi-cylinders include acorresponding number of guide slots for receiving a respective one ofsaid guide pins for controlling the displacement of said cutter bar. 9.The method of claim 8, wherein said engagement rods engage saidsemi-cylinders through said cap to provide a pushing force, to displacethe semi-cylinders in a substantially axial direction of the guide tubeand the cutter bar in a substantially radial direction of the guidetube.
 10. The method of claim 9, wherein said cap includes a shankextending therefrom away from said guide tube and a power source iscapable of being connected to said shank to rotate said guide tube andcutter bar for cutting the bone.
 11. The method of claim 10, whereinsaid engager is positioned on said shank and said engagement rods extendsubstantially parallel to said shank.
 12. The method of claim 10,wherein the undercut reamer is capable of cutting circular grooves orspiral grooves in the internal surface of the bone to a increasefixation strength between the bone and the endoprothesis.
 13. The methodof claim 1, wherein said guide tube includes at least one opening in aside wall thereof for receiving said at least one cutter of said cutterbar.
 14. The method of claim 13, wherein said at least one cutterextends out through said at least one opening in the guide tube exposingsaid at least one cutter to cut at least one groove on the internalsurface of the bone.
 15. The method of claim 14, wherein said at leastone cutter is retractable through said at least one opening in saidguide tube to disengage said cutter from the bone after cutting,allowing the reamer to be removed from the bone before placement of theendoprothesis.